Wavelength division multiplexing optical communications technology is used in the high-speed large-capacity optical networks that support the high level of data communications needed in today's society. There has been progression in the introduction of reconfigurable optical add drop multiplexers (ROADM devices) having reconfigurable add and drop functions at optical nodes, which are equivalent to branches in an optical network. To realize ROADM devices, wavelength selective switches (also called wavelength selective optical switches), which can switch any wavelength in any direction, have gained attention. Light beam deflection elements which select a wavelength and deflect light beams to a desired output port have been used in wavelength selective optical switches, and in Patent References 1 and 2, the diffraction phenomenon by liquid crystal on silicon (LCOS) is used. Furthermore, in Patent References 3 and 4, something which utilizes mechanical displacement of a mirror array of a micro-electro-mechanical system (MEMS) is used.